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[Linux-cluster] Startup and Shutdown of a Virtual/Physical cluster

After a period of time experimenting with a cluster composed of 3 physical
nodes hosting 5 XEN guests, both physical and virtual nodes being part of
their respective cluster, with shared storage based on iSCSI and GFS, I am
quite satisfied with the system stability and performances.

My concern now is with the management of the startup of the cluster (and
possibly also shutdown, imagine an UPS stating that the energy is

When the physical cluster starts up, and the nodes are operational, the
virtual nodes are started in an unordered mode, e.g. the allocation to the
physical nodes is not predetermined. If the physical cluster nodes come up
at different times, the first operational node of the physical cluster
tries to bring up all the virtual guests, even if the available memory is
not sufficient. This causes some instabilities at system startup, and
requires some manual intervention in order to distribute the xen guests
among the physical cluster nodes.

Is there some way to prevent this kind of behaviour ?

Another aspect is related to system shutdown. My system is powered by an
UPS, but once in a year due to maintenance on the power supply it may
happen that there is need to shutdown the system, or in case of blackout
with a long time. How is it possible to completely shutdown the cluster by
UPS command ?

Thanks, Paolo

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